lib/i915_drm_local: Add I915_GEM_CREATE_EXT_FLAG_NEEDS_CPU_ACCESS

For now dump into i915_drm_local.h. Once the uapi on the kernel side is
merged, and is part of drm-next, we can sync the kernel headers and
remove this.

Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Reviewed-by: Nirmoy Das <nirmoy.das@intel.com>

1 files changed, 21 insertions, 0 deletions

diff --git a/lib/i915/i915_drm_local.h b/lib/i915/i915_drm_local.h
index 9a2273c4..ac35abf6 100644
--- a/lib/i915/i915_drm_local.h
+++ b/lib/i915/i915_drm_local.h
@@ -23,6 +23,27 @@ extern "C" {
 
 #define DRM_I915_QUERY_GEOMETRY_SUBSLICES      6
 
+/*
+ * Signal to the kernel that the object will need to be accessed via
+ * the CPU.
+ *
+ * Only valid when placing objects in I915_MEMORY_CLASS_DEVICE, and only
+ * strictly required on platforms where only some of the device memory
+ * is directly visible or mappable through the CPU, like on DG2+.
+ *
+ * One of the placements MUST also be I915_MEMORY_CLASS_SYSTEM, to
+ * ensure we can always spill the allocation to system memory, if we
+ * can't place the object in the mappable part of
+ * I915_MEMORY_CLASS_DEVICE.
+ *
+ * Without this hint, the kernel will assume that non-mappable
+ * I915_MEMORY_CLASS_DEVICE is preferred for this object. Note that the
+ * kernel can still migrate the object to the mappable part, as a last
+ * resort, if userspace ever CPU faults this object, but this might be
+ * expensive, and so ideally should be avoided.
+ */
+#define I915_GEM_CREATE_EXT_FLAG_NEEDS_CPU_ACCESS (1 << 0)
+
 #if defined(__cplusplus)
 }
 #endif